Ultimate guide to the multiverse

WHETHER we are searching the cosmos or probing the subatomic realm, our most successful theories lead to the inescapable conclusion that our universe is just a speck in a vast sea of universes.

Until recently many physicists were reluctant to accept the idea of this so-called multiverse. Recent progress in cosmology, string theory and quantum mechanics, though, has brought about a change of heart. “The multiverse is not some kind of optional thing, like can you supersize or not,” says Raphael Bousso, a theoretical physicist at the University of California, Berkeley. Our own cosmological history, he says, tells us that “it’s there and we need to deal with it”.

These days researchers like Bousso are treating multiverses as real, investigating them, testing them and seeing what they say about our universe. One of their main motivations is the need to explain ...

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